This invention relates to a dispenser used in liquid deposition devices, and more particularly to a high speed, high precision glue dispenser that is responsive to sheets of material passing through it such that adhesive can be deposited onto sheets of varying thickness passing through the glue dispenser without manual intervention or loss of contact between the sheets and the dispenser, even if the sheets demonstrate non-planar attributes.
Automated gluing systems are routinely used to affect high-speed, repeatable application of adhesives to various substrates. This practice has been used extensively in the manufacture of paper and related products, such as corrugated cardboard, where devices known as flexo folder gluers receive one or more sheets to have them printed, die cut, glued and folded. While in the gluing station portion of the flexo folder gluer, the sheet has one or more rows of continuous adhesive lines or discontinuous adhesive dots deposited onto one or more of its flap surfaces as it travels past a glue applicator head. In a conventional gluing station, the sheet is fed into a gap along a preferred path such that an aligned valve and nozzle can be actuated to deposit a stream of the adhesive onto the desired location on the sheet. The one or more valves are securely mounted to a support structure, such as a mounting plate to ensure consistent adhesive application. While this works well for its intended purpose, it tends to be inflexible in terms of changing the valves out when service is required. In addition, by rigidly fixing the gap spacing, the system is not well-suited to accommodating sheets that demonstrate non-planar attributes (such as curled, warped or related surface undulations), or sheets of differing thickness, as thin sheets tend to float or bounce around, while thick substrates tend to pinch, causing substrate misalignment and subsequent compromise of adhesive deposition.
One way to avoid the inaccuracies and down-time of a fixed applicator is to incorporate a “floating” dispenser, where the dispensing member is movable relative to the rest of the applicator due to the use of a slide bearing. While these help reduce the incidence of pinching and subsequent jamming of sheets as they pass by the dispenser, the repeated, intermittent periods of non-contact between the head and the sheets being glued does not adequately allow the system to purge any residual glue from the discharge apertures located on the applicator head. This makes the head prone to the buildup of dried, hardened glue around its discharge apertures, which leads to a concomitant decrease in glue deposition quality.
What is needed is a glue dispenser that can adjust automatically to travelling sheets with surface undulations or of differing thickness without requiring the user to adjust the mechanism or otherwise interrupt operation of the machine. What is additionally needed is a way to keep the passing sheet in constant contact with the applicator head during glue deposition without too tight of a fit to promote accurate, repeatable glue application to sheets of differing thickness.